The latest analysis of the Global Burden of Disease, Injuries and Risk Factors study (GBD), assessing data ranging from 1990–2021, has indicated that roughly half of all healthy years of life lost due to stroke worldwide are caused by haemorrhagic stroke—despite it being almost half as common as ischaemic stroke.
The analysis revealed that, with 81 million healthy years of life having been lost, haemorrhagic strokes were responsible for half of all stroke-related disability and lives lost globally in 2021. The most affected people were found to be those aged 70 years and younger—as well as those living in low-income countries, where the proportion of strokes characterised by intracerebral haemorrhage (ICH) is double compared to high-income countries (37% vs 18%, respectively).
In addition, regarding the major drivers of stroke across the globe, the GBD analysis’ investigators report that—“for the first time”—their study suggests ambient particulate matter air pollution is a top risk factor for subarachnoid haemorrhage (SAH), currently contributing to 14% of the death and disability caused by this stroke subtype at a rate that is comparable to smoking.
More broadly, the researchers conclude that the worldwide stroke burden has undergone a rapid rise since 1990, with ageing and growing populations as well as a significant increase in people’s exposure to environmental and behavioural risk factors being among the key drivers escalating stroke’s prevalence today.
These findings were recently published in The Lancet Neurology and are also set to be presented at next month’s World Stroke Congress (WSC; 23–26 October, Abu Dhabi, United Arab Emirates).
Rapid rise of stroke burden
Although stroke is now considered a highly preventable and treatable condition, this newly published GBD analysis provides evidence that there has been a notable uptick in the global burden of the condition over the past three decades.
Across the globe, the number of people having a new stroke rose to 11.9 million in 2021—a 70% increase from 1990. In addition, the number of stroke survivors rose to 93.8 million (up 86% versus 1990) and stroke-related deaths rose to 7.3 million (up 44% versus 1990), making the condition the third most common cause of death worldwide in 2021, behind ischaemic heart disease and COVID-19. More than three quarters of those affected by stroke live in low- and middle-income countries (LMICs), the GBD analysis also found.
The number of disability-adjusted life years (DALYs) lost to stroke was observed to have increased by 32% between 1990 and 2021, with the estimated amount of healthy life lost growing from 121.4 million years to 160.5 million years—making stroke the fourth leading cause of worldwide health loss after COVID-19, ischaemic heart disease, and neonatal disorders.
Investigators for the GBD analysis conclude that the burden of stroke is rising due in no small part to population growth and the prevalence of ageing populations across the globe. However, they also identify a number of preventable environmental, metabolic and behavioural risk factors that have “increased substantially” and contributed to rising stroke numbers from 1990 to 2021. Examples include an 88% increase in high body mass index (BMI), a 72% increase in high temperatures, and a 32% increase in high blood sugar rates.
And, while accounting for the impact of demographics via ‘age standardisation’ revealed that there was a trend towards lower worldwide rates of stroke incidence (down 22%), prevalence (down 8%), deaths and DALYs (both down 39%) across almost every level of country income between 1990 and 2021, the investigators ultimately found that improvements in global incidence rates have “stagnated” since 2015. In addition, age-standardised rates of stroke incidence and prevalence, as well as stroke-related death and DALYs, have worsened across Southeast Asia, East Asia and Oceania, and also in people younger than 70 years of age.
“The global growth of the number of people who develop stroke—and died from or remain disabled by stroke—is growing fast, strongly suggesting that currently used stroke prevention strategies are not sufficiently effective,” said Valery Feigin (Auckland University of Technology, Auckland, New Zealand), lead author of the recently published analysis. “New proven-effective, population-wide and motivational, individual prevention strategies that could be applied to all people at risk of having a stroke, regardless of the level of risk—as recommended in the recent Lancet Neurology Commission on Stroke—should be implemented across the globe urgently.”
Discrepancies and risk factors
The present study has revealed that, in 2021, there were “striking differences” in the overall stroke burden between world regions and national income levels. In high-income areas in North America and Australasia, and middle-income parts of Latin America—regions with the lowest stroke burden—the age-standardised rates of incidence and prevalence were lowest in New Zealand (67.8 and 707.4 per 100,000 people, respectively); death rates were lowest in Canada (20.4 per 100,000 people); and DALY rates were lowest in Australia (435 per 100,000 people). In contrast, in low- and middle-income regions of East and Central Asia, and also sub-Saharan Africa, the rates of incidence, prevalence, death and DALYs were between two and 10 times higher (more than 248, 1,458, 190 and 4,320 per 100,000 people, respectively) in 2021.
“Stroke-related health loss disproportionately impacts many of the most disadvantaged countries in Asia and sub-Saharan Africa due to the growing burden of uncontrolled risk factors, especially poorly controlled high blood pressure, and rising levels of obesity and type 2 diabetes in young adults, as well as the lack of stroke prevention and care services in these regions,” explained co-author Catherine Johnson (Institute for Health Metrics and Evaluation [IHME], Seattle, USA). “The shift in stroke burden towards younger populations is likely to continue unless effective preventive strategies are implemented urgently.”
The investigators found that metabolic risk factors—especially high BMI, high systolic blood pressure and high low-density lipoprotein (LDL) cholesterol—contributed to the greatest level of stroke burden across all country income levels, ranging from 66–70%, in 2021. This was followed by environmental risk factors collectively—including air pollution, low/high ambient temperature and lead exposure—in LMICs, ranging from 35–53%. Overall, in 2021, the five leading global risk factors for stroke were high systolic blood pressure, particulate matter air pollution, smoking, high LDL cholesterol, and household air pollution, with considerable variation by age, sex and location.
Alongside their finding that ambient particulate matter air pollution is now a leading risk factor for SAH, the investigators report that “substantial progress” has been made in reducing the overall global stroke burden from risk factors linked to poor diet, air pollution, and smoking, with rates of health loss due to diets high in processed meat and low in vegetables declining by 40% and 30%, respectively, particulate matter air pollution dropping by 20%, and smoking decreasing by 13%, from 1990 to 2021. This suggests that strategies to reduce exposure to these risk factors over the past three decades—such as clean air zones and public smoking bans—have been successful, the researchers aver.
Opportunities for progress
Among other key findings from the GBD analysis is an estimation that the global number of stroke-related DALYs, attributable to a total of 23 different risk factors, has risen from 100 million years of healthy life lost in 1990 to 135 million in 2021—presenting “a public health challenge and an opportunity for action”. The largest proportions of these risk factors are found in Eastern Europe, Asia, and sub-Saharan Africa, according to the researchers.
“With 84% of the stroke burden linked to 23 modifiable risk factors, there are tremendous opportunities to alter the trajectory of stroke risk for the next generation,” Johnson added. “Given that ambient air pollution is reciprocally linked with ambient temperature and climate change, the importance of urgent climate actions and measures to reduce air pollution cannot be overestimated. And, with increasing exposure to risk factors such as high blood sugar and diet high in sugar-sweetened drinks, there is a critical need for interventions focused on obesity and metabolic syndromes. Identifying sustainable ways to work with communities to take action to prevent and control modifiable risk factors for stroke is essential to address this growing crisis.”
The authors also believe that, through implementing and monitoring the evidence-based recommendations set out in the 2023 World Stroke Organization-Lancet Neurology Commission on Stroke, there is an opportunity to “drastically reduce” the global burden of stroke in this decade and beyond, as well as improve brain health and the overall wellbeing of millions of people around the world.
According to Feigin, “additional and more effective” stroke prevention strategies “must be urgently implemented across all countries”—including task-shifting from doctors to nurses and health volunteers; the wider use of evidence-based mobile and telehealth platforms; pragmatic solutions to address critical gaps in stroke service delivery; workforce capacity building; and epidemiological surveillance systems.
